Hopefully, you are aware of the possibility of “long-hauling”; the practice of some Las Vegas taxi drivers to take patrons arriving at McCarran International Airport to their hotel via a longer route than necessary. This is frequently called “tunneling”, too since it usually involves going through the tunnel to I-215 even if your hotel is on the Strip.  As a general rule, if you are staying North of the airport, taking the I-215 tunnel will result in traveling 3 extra miles and a higher fare.  This includes the Strip and downtown.  There are occasions where it might result in getting to your destination faster, but it is rare that the time difference is more than a minute or so.  Two ways to prevent being long-hauled are to know where you are going and to tell the driver to take the shortest distance.  If you have been long-hauled, make sure to get the driver’s name and permit number.  If you are uncomfortable confronting the driver, you can file a complaint with the Taxicab Authority at (702)668-4000 or online.
Here are a few Google Maps examples showing the difference in distance and estimated time for a few routes.
McCarran to Golden Nugget
McCarran to Mirage
McCarran to Harrah’s
McCarran to Rio

Now it looks like the Las Vegas Taxicab Authority is beginning to take some proactive measures to deter it, too. http://www.lasvegassun.com/news/2012/jun/06/taxicab-authority-sets-checkpoints-crack-down-long/